Cell-to-cell communication is required for many biological processes such as differentiation, proliferation, and homeostasis. One system utilized by a wide range of eukaryotes is the Notch-signaling pathway. This pathway, especially the Notch receptor, is also critical for functional tumor angiogenesis. Thus, inhibition of Notch receptor function, blockage of the Notch receptor, and/or blockage of the Notch-signaling pathway are potential strategies for anti-cancer compositions and therapies. Small molecule inhibitors of the Notch receptor have proven to be toxic because they suppress wild type (normal) tissue expression of Notch receptors throughout the body. Thus, different members of the Notch-signaling pathway should be considered as potential targets for therapeutics.
A vasculature ligand for the Notch receptor is Delta 4 or Delta-like 4 (DLL4). Largely expressed in the vasculature, DLL4 is critical for vascular development (Yan et al., Clin. Cancer Res., 13(24): 7243-7246 (2007); Shutter et al., Genes Dev., 14(11): 1313-1318 (2000); Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Krebs et al., Genes Dev., 14(11): 1343-1352 (2000)). Mice heterozygous for DLL4 are embryonically lethal due to major defects in vascular development (Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Duarte et al., Genes Dev., 18(20): 2474-2478 (2004); Krebs et al., Genes Dev., 18(20): 2469-2473 (2004)). The expression of DLL4 can be induced by VEGF (Liu et al., Mol. Cell Biol., 23(1): 14-25 (2003); Lobov et al., Proc. Natl. Acad. Sci. USA, 104(9): 3219-3224 (2007)). In turn, DLL4 can negatively regulate VEGF signaling, in part through repressing VEGFR2 and inducing VEGR1 (Harrington et al., Microvasc. Res., 75(2): 144-154 (2008); Suchting et al., Proc. Natl. Acad. Sci. USA, 104(9): 3225-3230 (2007)). Exquisite coordination between DLL4 and VEGF is essential for functional angiogenesis.
In addition to its physiological role, DLL4 is up-regulated in tumor blood vessels (Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Mailhos et al., Differentiation, 69(2-3): 135-144 (2001); Patel et al., Cancer Res., 65(19): 8690-8697 (2005); Patel et al., Clin. Cancer Res., 12(16): 4836-4844 (2006); Noguera-Troise et al., Nature, 444(7122): 1032-1037 (2006)). Blockade of DLL4 potently inhibited primary tumor growth in multiple models (Nogucra-Troisc et al., Nature, 444(7122): 1032-1037 (2006); Ridgway et al., Nature, 444(7122): 1083-1087 (2006); Scehnet et al., Blood, 109(11): 4753-4760 (2007)). The inhibition of DLL4 was even effective against tumors that are resistant to anti-VEGF therapy. The combinatorial inhibition of both DLL4 and VEGF provided an enhanced anti-tumor activity. Interestingly, unlike VEGF inhibition that reduces tumor vessel formation, DLL4 blockade leads to an increase in tumor vasculature density wherein the vessels are abnormal, cannot support efficient blood transport, and are effectively nonfunctional. Thus, DLL4 provides a potential target for cancer treatment.
There is a need in the art for therapeutic agents capable of targeting the DLL4-Notch pathway and thereby inhibiting, or even preventing, tumor angiogenesis and growth.